Lifetime of LCD panels and polarizers has become an important factor in recent years as they are used in LCD units operated at higher brightness and higher contrast. Particularly, since films of polarizers are exposed to intense short wavelength light in the blue band, they are often burnt by the light. To cope with this problem, inorganic polarizers have been developed. A typical inorganic polarizer is a wire-grid type polarizer, MOXTEK, manufactured by MOXTEC Inc. This polarizer is a so-called reflective polarizer, which allows transmission of light that is polarized in a particular direction but reflects the rest of the light. As a consequence, the polarizer suffers little time degradation due to irradiation of light and is often used in a projection type LCD, particularly a rear projection TV requiring a long lifetime.
However, reflective inorganic polarizers have a disadvantage that they have a lower polarization degree than conventional absorptive organic polarizers (for example, dye-polarizers). To overcome the disadvantage, a reflective inorganic polarizer is coupled with a phase retardation plate, called an optical compensator, to enhance the contrast of a displayed image.
There is disclosed in Japanese Patent Application Laid Open No. 2000-356770 an LCD panel having on the light-incidence side thereof an absorptive polarizer, which is provided on the light-incidence side thereof with a reflective polarizer.
However, as compared with conventional absorptive organic polarization films, such a reflective inorganic polarizer as mentioned above causes (1) degradation of contrast, (2) repetitive or multiple reflections of unwanted components of light between a thin metallic layer incorporated in the LCD panel to form a black matrix of the LCD panel and the reflective inorganic polarizer, which reflection in turn causes light to partly enter the reflective inorganic polarizer and results in several irregular linear patterns on the display screen. These factors deteriorate the picture quality of a displayed image. Particularly, when an optical compensator is provided on the light-incidence side of an LCD panel to enhance the contrast of a displayed image, a linearly polarized beam of light is partly depolarized into a beam of elliptically polarized light, which includes two linearly polarized lights oscillating in two perpendicular directions. Together with the multiple reflections, this elliptical polarization significantly degrades the picture quality.